U.S. patent application number 11/900415 was filed with the patent office on 2008-04-24 for intelligent monitoring system and method for mill drives in mineral grinding processes.
This patent application is currently assigned to UNIVERSIDAD TECNICA FEDERICO SANTA MARIA. Invention is credited to Jaime Jose Rebolledo Campos, Ricardo Antonio Araya Cereceda, Esteban Marcelo Cid Gonzalez, Jorge Antonio Pontt Olivares.
Application Number | 20080097723 11/900415 |
Document ID | / |
Family ID | 39264217 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080097723 |
Kind Code |
A1 |
Pontt Olivares; Jorge Antonio ;
et al. |
April 24, 2008 |
Intelligent monitoring system and method for mill drives in mineral
grinding processes
Abstract
The present invention refers to an intelligent monitoring system
and method of a 12-pulse LCI drive that controls the motors in
charge of driving SAG and ball mills present in the mineral
grinding process. It includes a monitoring module which is able to
efficiently determine the origin of certain types of failures,
which allows solving the problem in a quick manner based on the
topology knowledge of the 12-pulse LCI drive which is being
monitored. The system and method also determines and identifies the
overall operation state of the 12-pulse LCI drive by an inspection
of the variables related with the control loop in a way to identify
control adjustments malfunction as well as the inspection of the
symmetric operation of the 6-pulse LCI drives which conform the
12-pulse LCI drive.
Inventors: |
Pontt Olivares; Jorge Antonio;
(Valparaiso, CL) ; Campos; Jaime Jose Rebolledo;
(Valparaiso, CL) ; Cid Gonzalez; Esteban Marcelo;
(Valparaiso, CL) ; Cereceda; Ricardo Antonio Araya;
(Valparaiso, CL) |
Correspondence
Address: |
Eric A. Hanscom, Esq.;Law Offices of Eric Hanscom
7395 Portage Way
Carlsbad
CA
92011
US
|
Assignee: |
UNIVERSIDAD TECNICA FEDERICO SANTA
MARIA
Valparaiso
CL
|
Family ID: |
39264217 |
Appl. No.: |
11/900415 |
Filed: |
September 10, 2007 |
Current U.S.
Class: |
702/182 ; 241/36;
700/108 |
Current CPC
Class: |
B02C 17/1805
20130101 |
Class at
Publication: |
702/182 ;
241/036; 700/108 |
International
Class: |
B02C 25/00 20060101
B02C025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2006 |
CL |
CL 2390-2006 |
Claims
1. Intelligent Monitoring System of 12-pulse LCI drive that
controls the motors in charged of driving SAG and ball mills that
are present in the mineral grinding process compromising: a drive
short-circuit detection technique that compromises measuring
conductivity state signals of each semiconductor of the 12-pulse
LCI drive; a technique to determine the overall electrical drive
operation state that compromises measuring voltage and current
signals at different locations of interest in the mentioned
drive.
2. The intelligent monitoring system of claim 1, wherein the
technique compromises adapting the measured signals, acquiring the
adapted signals, identifying the conduction pattern of the 12-pulse
LCI drive, and comparing with correct commutation pattern.
3. The intelligent monitoring system of claim 2, wherein it
additionally compromises generating a warning if a short-circuit
occurs.
4. The intelligent monitoring system of claim 3, wherein it
additionally compromises performing programmed actions if a
short-circuit occurs.
5. The intelligent monitoring system of claim 1, wherein the module
that determines the overall operation state of the 12-pulse LCI
drive compromises the adapting the measured signals, calculating
RMS values of the acquired signals, determining the operation state
(O.S.) in which the drive finds itself, comparing the measured
values with the operation intervals corresponding to the O.S.
6. The intelligent monitoring system of claim 5, wherein it
additionally compromises generating an output report.
7. An intelligent monitoring method of a 12-pulse LCI drive that
control the motors in charged of driving the SAG and ball mills
present in the mineral grinding process, wherein the method
compromises the following steps: detecting drive short-circuits in
the 12-pulse LCI drive, measuring the conduction state of each
semiconductor of the 12-pulse LCI drive; and also monitoring the
overall operation state of 12-pulse LCI drive that compromises
measuring voltage and current signals at different locations of
interest in the mentioned drive.
8. The intelligent monitoring system of claim 7, wherein the
short-circuit detection stage compromises adapting the measured
signals; acquiring the adapted signals; identifying the conduction
pattern of the 12-pulse LCI drive; and comparing with correct
commutation logic of a 12-pulse LCI drive.
9. The intelligent monitoring system of claim 8, wherein it
additionally compromises generating a warning if a short-circuit
occurs.
10. The intelligent monitoring system of claim 9, wherein it
additionally compromises performing programmed actions if a
short-circuit occurs.
11. The intelligent monitoring system of claim 7, wherein the stage
of monitoring the overall drive operation state of the 12-pulse LCI
drive compromises adapting the measured signals; acquiring the
adapted signals; calculating RMS values of the acquired signals;
determine the operation state (O.S.) in which the drive finds
itself; and comparing the measured values with the operation
intervals corresponding to the O.S.
12. The intelligent monitoring system of claim 11, wherein it
additionally compromises generating an output report.
Description
FIELD OF THE INVENTION
[0001] The present invention consists of an intelligent monitoring
system and method for driving a mineral grinding mill and more
specifically, intelligent monitoring of a kind of converter named
12-pulse Load Commutated Inverter (LCI) which controls the motor in
charge of driving the semi-autogenous (SAG) mills and steel balls
present in the mineral grinding process.
BACKGROUND OF THE INVENTION
[0002] Chile's most important natural resource, from the economical
and business point of view, is copper. Chile has a large number of
mines operating over 2000 meters above sea level which implies
using expensive electrical and mechanical machinery. Since Chile is
mainly an exploiter of natural resources, acquisition of expensive
expert support is required in most cases of operational failure,
which adds up to unavoidable losses due to partial or full
production paralyzation.
[0003] Among the different processes carried out in copper mining
one of the most important processes is fine mineral grinding.
Minerals that come from the crushing stage enter the SAG mills and
steel balls, which have the function of drastically reducing the
size of the mineral, to proceed afterwards to the flotation
process. In this process of fine grinding the most relevant
equipment are the SAG mills and steel balls which are driven by
huge synchronic motors (of up to 20 MW). These are controlled
electrically by power converters, cycloconverters (CCV) or
load-commutated inverters (LCIs) among others. Despite the
electrical drive controls mill drive other monitoring systems are
used additionally which register real-time variables of the mill,
as well as of the electrical variables of the electrical drive. The
objective of this monitoring is to have readings available of what
is occurring and also register events that could happen, such as
failures or non-scheduled stops, providing information for
afterward analysis.
[0004] Among the most used solutions nowadays is the device
"Transient Recorder" from the company ABB. This equipment
determines if the electrical control functions properly by
evaluating the monitoring of mechanical and electrical signals
according to criteria and limits established by the manufacturer.
This device has a rigid and closed composition and structure, that
is to say, it is only compatible with other ABB equipment making it
a nonflexible device. It does not allow for modifications according
to drive requirements.
[0005] SIEMENS has a system called "Totally Integrated Automation
(TIA)", which allows the efficient automation of any industrial
production process. It is not specific or an expert on electrical
drives, additionally it is only based on proprietary software and
hardware of SIEMENS.
[0006] Besides these commercial products there are patents directly
or indirectly related to the monitoring of mill drives. Among those
that directly relate with the proposed Monitoring System, is the
U.S. Pat. No. 4,404,640, titled "Grinding mill monitoring
instrumentation" of Robert F. Dumbeck and Phillip W. Welch, which
describes an invention that monitors different operation conditions
of a ball mill, displaying on a screen the mill operation and
storing data to have a register. The instrumentation used for this
case corresponds only to current transformers (CT) which are
coupled to the motor feed. These transformers sense the current
that flows through the motor and this measurement is employed to
obtain the power developed by the mill. Besides this signal, the
information of mineral flow through the mill is available with
which the efficiency of the equipment is estimated and
optimized.
[0007] Another related patent is U.S. Pat. No. 5,698,797 titled
"Device for monitoring a ball grinder" of Daniel Fontanille and
Jacques Barbot which describes the continuous monitoring of three
parameters of the ball mill operation: a) quantity of mineral, b)
amount of balls, c) wear of the armor plating inside the walls of
the mill. To do this, the proposed device employs an
electromagnetic wave emitter placed inside the mill and at least
one electromagnetic wave receiver placed close to the mill. Using
the angular placement of the receiver as well as other special
electronic devices, it is capable of detecting the mentioned
parameters of the ball mill operation.
[0008] The U.S. Pat. No. 6,874,366 titled "System to determinate
and analyze the dynamic internal load in revolving mills, for
mineral grinding" of Luis Magne, Waldo Valderrama, Jorge Pontt,
Ennio Perelli, Claudia Velasquez and German Sepulveda (patent
pending CL 189-03), describes a system as a method to measure in a
direct, dynamical and online way different parameters related to
the internal dynamic load of a mill when in operation. The system
is basically composed of wireless acoustic sensors that are coupled
to the mill, receivers and conditioning units that are located
close to the mill and communication and processing units. The
output signals of the system are transmitted to the central control
system. The main objective of this invention is to increase the
efficiency of the grinding process as well as the availability of
the equipment. To achieve this, the total internal load of the mill
(of both balls and mineral) is monitored moreover the apparent
density of the mill's internal load.
[0009] Other patents related indirectly with the proposed invention
are presented in the following sections. The U.S. Pat. No.
6,577,987 titled "Operational monitoring for a converter" of Guido
Wenning describes a generic operational monitor. It bases itself on
comparing a mean value with a stored reference value. According to
the proposed method, al least two comparisons are needed (one
considering the input signal and the other the output signal) which
are contrasted to their respective references (with a certain
tolerance). This generates a state signal for each comparison,
which in turn are evaluated in a central evaluation unit to
determine the operational state of the converter.
[0010] Other patents that are indirectly related to the proposed
invention are the ones that reference mill control instead of mill
monitoring. Although this difference is relevant, these patents
contribute well to the conception of monitoring methods, given that
to obtain control of the mill it is necessary to have a good
monitoring system of its variables.
[0011] In this manner, the U.S. Pat. No. 4,611,763 titled "Method
and apparatus for controlling a grinding mill" of Hiroshi Tomiyasu,
Masahiro Hattori and Yoshio Itoh, describes an apparatus as a
method to automatically control a mill, having as an objective the
maximization of its efficiency. The system includes a grinding
mill, a raw material feed apparatus and a controller, which receive
signals from the mill and uses them as inputs, comparing them to
its respective references. Based on this, the controller generates
an output which is used as an input signal for the raw material
feed apparatus. This signal is updated by an integrator which
modifies the reference signal after a given time.
[0012] The U.S. Pat. No. 4,586,143 titled "Grinding mill control
system" of Robert F. Dumbeck and Phillip W. Welch describes the
capacity to process multiple signals that originate from a ball
mill and the relationship among them. Analysis of variations of the
flow of material through the mill generates control actions so that
mill operates close to its optimum work point which is defined
previously.
[0013] The proposed invention has a direct relationship with these
kinds of monitoring and supervision systems. These systems are
presently available in the market but only focused on monitoring
how the electric system functions by registering electric
variables. The new intelligent monitoring system for 12-pulse LCI
drive used in mineral grinding mill, proposes a method and its
implementation that offers a detailed monitoring with new
functionalities that can be personalized according to specific
needs. In this manner, it is possible to perform similar functions
to the ones that exist in a conventional monitoring system.
Additionally it is possible to identify a determined type of
failures and infer the overall drive operation state of the mill
based on a comparison of online measurements and theoretical
behavior. As a result of this, there is a significant and clear
difference and improvement with respect to the existing systems
that are commercialized.
BRIEF SUMMARY OF THE INVENTION
[0014] The present invention is an intelligent system and method
for monitoring a 12-pulse LCI drive used in mineral grinding
operation. Specifically this monitoring system corresponds to an
electronic device that is ideally installed close to the electrical
drive of a SAG or ball mill, which monitors its operation
status.
[0015] This device as such is an industrial computer that
incorporates hardware and software that is specialized in external
signal acquisition and processing. The drive signals that are
monitored are normally available from the same drive control, thus
avoiding additional hardware for measuring (sensors). Nonetheless,
along with the classic monitoring variables (input and output
voltages and currents) the system requires signals that have the
conduction state information for each semiconductor from 12-pulse
LCI drive for the short-circuit surveillance. Thus, some
applications may need to include some hardware associated to this
requirement.
[0016] Concerning the method, this system includes an application
specifically developed for this monitoring system. This method
contemplates 4 main functions which may be adapted and personalized
depending on the needs or applications in which the monitoring
system is employed. These functions are:
[0017] A) Monitor and register abnormal operation conditions
(failures) of a 12-pulse LCI drive.
[0018] B) Historical registry of some electrical variables of
interest of a 12 pulse LCI drive.
[0019] C) Short-circuit detection in 12-pulse LCI drive
operation.
[0020] Besides these functions, the system provides a visualization
screen for the monitored variables, as well as storage on a hard
drive. Configuration and system operation via Ethernet is also
available.
[0021] When high power drives and electrical machinery are used in
conjunction with mechanical equipment of big size, weight and
inertia it is necessary to perform constant maintenance. This
allows maintaining a high availability of the equipment and
diminishes the probability of coming out of service (consequence of
the large amount of potential failures that could present
themselves due to the complexity of the system). Regardless of all
the equipment maintenance, the probability of failure is not
completely eliminated. Thus, one of the biggest problems is to
identify these failures; its location and finally determine its
origin and solution in a quick and effective manner. Taking into
consideration the fact that the mining industry is developed at
reasonably high altitudes of hard access, it is not feasible to
have immediate assistance of the specialized technical support. All
this makes the trustworthiness and availability of key production
equipment one of the main objectives of planning. Thus the
intelligent system and method for monitoring a 12-pulse LCI drive
for mineral grinding has a main objective of providing a monitoring
system with classical functions as well as innovative ones in such
a way to supply more and better information on drive operation.
[0022] When incorporating intelligent monitoring it is possible to
determine the origin of certain types of failures based on the
knowledge of the 12-pulse LCI drive topology that is monitored.
[0023] In this manner a classical monitoring system is available
but with a new functionality related with a efficient detection of
a certain kind of failures associated with malfunction on
semiconductors of a 12-pulse LCI drive which permits a quick
solution for the problem.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates a power circuit of a 12-pulse Load
Commutated Inverter (12-pulse LCI) which feeds a synchronic motor.
This configuration is one of the most classically used for mineral
grinding circuits (background art).
[0025] FIG. 2 illustrates a block diagram of an intelligent
monitoring system in conjunction with the 12-pulse LCI drive
control. This figure illustrates the interconnection between the
intelligent monitoring system and the 12-pulse LCI drive
control
[0026] FIG. 3 shows a detailed block diagram of the intelligent
monitoring system for a 12-pulse LCI drive used in mineral grinding
applications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] To achieve a better description of the present invention an
explanation of its functioning is given based on the monitoring of
a 12-pulse LCI inverter.
12-Pulse LCI
[0028] This drive (FIG. 2, background art) is made up of two
6-pulse LCI which are connected by two coupling transformer
secondaries (wye-delta connection). Each 6-pulse LCI drive is
composed by two bridge thyristors (6 Silicon Controlled Rectifier
SCR semiconductors each) connected in anti-parallel manner by a
continuous current link, which is stabilized by a reactor. The
three-phase system connects to the T1 transformer primary, fed by
its two secondaries to the two 6-pulse LCI. A synchronic motor is
fed from the primary of the T2 transformer, whose secondaries are
connected to the outputs of the two 6-pulse LCI.
Control System (20)
[0029] Each one of the two 6-pulse LCI has a control scheme
(inherent to the drive) that basically consists of three steps (See
FIG. 2): [0030] a) Control System (21): performs control based on
the reference speed of the motor (211) and the process signals
(212), which are received from the master control system, which in
turn delivers process signals (213). [0031] b) Signal Distribution
Module (22): Receives the electrical measurements from the two
6-pulse LCI, which in turn communicate with the control system
(21). On the other side, the control system (21) sends
firing-signals towards this module. Additionally this module
delivers the firing-signals to each pulse amplifier module (23).
The control system of the 12-pulse LCI drive described before
depends on the manufacturer. [0032] c) Firing-Pulse Amplification
(23): modules (one for each semiconductor) that receive a logical
firing signal and then amplify it applying an isolated current
pulse in the gate of each semiconductor to incite their ignition.
These modules can measure semiconductor conductivity as well as a
signal that acknowledges the correct generation of a current pulse.
Both signals are incorporated into the Intelligent Monitoring
System (10). Intelligent Monitoring System (10)
[0033] In parallel to the control scheme, the intelligent
monitoring system (10) receives analog measurements (sa1 and sa2)
from the two 6-pulse LCI in addition to the digital signals (sd1
and sd2) from the pulse amplifier modules (2 signals per
semiconductor). These signals go through an adjustment process in
which the digital (11) and analog (12) signals pass through an
adaptation phase compatible with acquisition system. Afterwards
there is a data acquisition stage (13) and data processing (14) and
finally, routines that execute the different monitoring and failure
detection tasks. Each one of these stages generate: information
that is displayed on a screen, temporary registers of electrical
variables, failure registers, etc.
[0034] It is important to point out that the coupling between the
intelligent monitoring system (10) and the control scheme (20) is
performed in a totally non-invasive manner. This mitigates the
effects that the disturbances of the intelligent monitoring system
may cause on the drive operation and vice versa.
[0035] This intelligent monitoring system (10) for this particular
case requires 32 analog and 48 digital signals that are provided by
the control system of the 12-pulse LCI drive. Both analog and
digital signals must be adapted for the following data acquisition.
Once the information is acquired these are made available to the
four main functions of the intelligent monitoring system, which are
detailed next:
[0036] a) Failure Storage (16): See FIG. 3. This function performs
the comparison among the measured value of a certain variable (161)
and its location in a range of values that are considered normal
(162). This value interval is generated by simulators or obtained
by field measurements. This comparison is performed in the time
domain, point to point, which allows adjusting the sensitivity of
the detection of abnormal conditions. This comparison generates a
trigger signal (163) that commands the circular buffer of a hard
disk (2). The objective of this is to be able to access data during
the interval when an abnormal condition appeared. Additionally this
function displays on a screen (1) the monitored variables.
[0037] b) Data Mining (17): This function allows monitoring the
analog variables of the system in RMS values (171). This requires
processing the acquired signals to obtain their RMS values. Once
this has been performed, these values are compared (172) to
reference values. This allows storing data in normal operation
conditions as well as abnormal operation conditions and during much
more time due to the smaller amount of data registered per cycle.
This function allows constructing a file of some drive variables of
interest. These variables are stored with statistic purposes that
may be employed additionally as a preventive indicator of some
operational drive failure or mill failure. It is also possible to
visualize these historic files on a display screen (1).
[0038] c) Intelligent Monitoring (18): this is the backbone of this
invention since it establishes the difference with the rest of the
existing alternatives in the market for monitoring grinding drives.
Specifically this function detects the origin and location of
certain types of failures such as problems with the semiconductor
commutation, failures provoked by the deterioration of the
semiconductors and firing circuits, and failures caused by
disturbances in the electrical feed network. All of these previous
situations cause a particular commutation pattern which is detected
by the intelligent monitoring system. Additionally the intelligent
monitoring system detects the overall drive operation state. To
perform both tasks it is necessary to implement two subtasks, which
are detailed next. [0039] c.1) Short-Circuit (SC) Failure Detection
(181): This module detects short-circuit in the 12-pulse LCI drive
through real-time monitoring of the conduction state of the
semiconductors, which are originated from the digital signals that
represent those states. This function monitors, detects and
identifies any uncharacteristic commutation of the drive that may
cause a short-circuit and drive failure. Each kind of drive has a
characteristic commutation pattern, thus when monitoring in
real-time the conduction state of the semiconductors, it is
possible to locate precisely the semiconductors that caused that
failure. [0040] c.2) Drive operation state (O.S) detection (182):
Comparison between an operational state detected of the drive with
an operational state condition considered as normal; speed
reference of the mill must be similar to the motor speed measured,
power developed by each 6-pulse LCI drive must be similar also,
checking this two task the control loop of the mill can be easily
verified and any commutation failure rejected which can provoke a
power unbalance in the drive.
[0041] d) Gate Test (15): normally after a drive general
maintenance it is necessary to test that it is functioning properly
before it is placed in service again. Thus it is necessary to
specifically check the firing pulses, the pulse amplifier modules
and the semiconductors. In the specific case of the LCI it is
normal to perform a Gate Test that consists of generating test
fires to corroborate the correct functioning of the hardware and
software associated to the power part of the system. This firing
pattern is generated using a special control routine provided by
the manufacturer, without having to place into service the drive.
This manual corroboration procedure is considerably slow since it
requires comparing a firing pattern considered normal with the
measurements obtained with a portable device. A solution for this
is to implement a procedure as part of the intelligent monitoring
system with a module called Gate Test (15). The Gate Test module
(15) allows testing all the semiconductors simultaneously and
displays on a screen (1) the results required for an electronical
comparison with a known pattern (background art). This block
requires two sources of data. The first corresponds to a
measurement performed on the firing pulses that control the
semiconductors, which are available in the digital signals (sd)
from the firing cards. These digital signals are stored for a
convenient amount of time in the firing pattern storage block
(151). Once stored, they need to be processed using a pattern
comparison algorithm (153). This comparison is done contrasting to
a known firing pulse pattern. If any electronic component should
fail in the semiconductor process control, this system will
identify the component that is presenting problems.
[0042] In addition to the four described functions, the display
screen (1) and data storage in hard disks (2), or similar storage
devices, exist.
* * * * *